The invention relates to a fastener driving tool for driving fasteners into a substrate, having a working piston that is capable of being moved abruptly translationally by igniting an ignitable mixture in a combustion chamber so as to drive a fastener, such as a stud or a nail, the volume of the combustion chamber being adjustable. The invention further relates to a method for operating such a fastener driving tool.
From German Patent Document DE 199 62 695 B4, a portable combustion-operated fastener driving tool is known that has a combustion chamber for receiving a combustion fuel mixture, the size of the combustion chamber being changeable in order to adjust the fuel gas mixture present therein towards lean or rich by means of axial displacement of a front-side combustion chamber wall. From German published patent application DE 10 2005 000 032 A1, a combustion-operated fastener tool is known that has two partial chambers, between which a divider is arranged, in which passageways have an active opening cross section.
The aim of the invention is to further improve the operation and/or energy efficiency of a fastener driving tool.
This aim is achieved in a fastener driving tool for driving fasteners into a substrate, having a working piston that is capable of being moved abruptly translationally by igniting an ignitable mixture in a combustion chamber so as to drive a fastener, such as a stud or a nail, the volume of the combustion chamber being adjustable, in that the fastener driving tool comprises a control device which is connected in control relationship to an adjusting device for adjusting the combustion chamber volume and to a metering valve device for metering fuel gas. The fastener driving tool according to the invention is preferably a portable combustion-operated fastener driving tool. In order to drive a fastener, gas, for example from a gas cartridge, is mixed in the combustion chamber with oxygen or air to form an ignitable mixture. When the ignitable mixture is ignited, it then abruptly expands so as to drive the working piston. As a result of combining, according to the invention, the adjusting device with the metering valve device, the fastener driving tool is capable of operating over a wide energy range while at the same time enabling efficient energy use. The load on the fastener driving tool during operation is markedly reduced, in particular when fasteners are driven at minimum energy. As a result, the serviceable life of the fastener driving tool is extended.
A preferred embodiment of the fastener driving tool is characterized in that the adjusting device for adjusting the combustion chamber volume comprises a motor, in particular an electric motor. Particularly preferably, the combustion chamber volume is adjusted using a stepper motor. The motor is controlled by the control device.
Another preferred embodiment of the fastener driving tool is characterized in that the motor is linked by a gear mechanism to an adjustable combustion chamber wall. The gear mechanism is preferably designed such that a self-locking mechanism causes the same to stay in the current position thereof when under load from the combustion chamber pressure. Additionally, the gear mechanism is preferably designed such that the combustion chamber pressure does not act on the motor. The motor is mounted in the fastener driving tool preferably with the aid of dampening elements.
Another preferred embodiment of the fastener driving tool is characterized in that the control device is connected to an operating device for energy adjustment and/or to an indicator device that indicates energy information. With the aid of the operating device, a user or operator is able to set a desired amount of driving energy in a simple manner. With the aid of the indicator device, the desired amount of driving energy can be indicated in a simple manner. Additionally, a minimally and a maximally possible amount of driving energy can be indicated with the aid of the indicator device. As a result, the ease of use of the fastener driving tool is markedly increased.
The aforestated aim is alternatively or additionally achieved by a method for operating an aforedescribed fastener driving tool, in which method both the combustion chamber volume and metering of the fuel gas flow into the combustion chamber are adjusted with the aid of the control device. As a result, the amount of energy provided in the fastener driving tool for the purpose of driving fasteners can be adjusted very quickly and efficiently. As a result, it is made possible in particular to drive a variety of fasteners into a variety of substrates without energy being wasted. Owing to the adjustment of both, the combustion chamber volume and the amount of fuel gas fed in, the mixing ratio in the combustion chamber can be optimally adjusted.
A preferred embodiment of the method is characterized in that the current actual combustion chamber volume is measured and compared with a desired target combustion chamber volume. The setting for the combustion chamber volume may be stored in the control device.
Another preferred embodiment of the method is characterized in that a control variable for the adjusting device for adjusting the combustion chamber volume is determined from deviations between the current actual combustion chamber volume and the desired target combustion chamber volume. The target combustion chamber volume is provided by the user or operator. The control variable determined is used to control the motor, with the aid of which the combustion chamber volume is adjusted.
Another preferred embodiment of the method is characterized in that the fastener driving tool has a reset function which is triggered by a user interaction and during which the setting of the combustion chamber volume and/or metering of the fuel gas flow into the combustion chamber is/are calibrated. The reset function is triggered, for example, as a result of a rechargeable battery or gas cartridge being inserted into the fastener driving tool.
Another preferred embodiment of the method is characterized in that during a reset the adjusting device for adjusting the combustion chamber volume is moved against a limit stop. During a reset the motor is moved against a limit stop, for example. On reaching the limit stop, the motor remains in the position adopted, for example because further adjustment is blocked or the motor is switched off.
Another preferred embodiment of the method is characterized in that the current actual combustion chamber volume is measured with the aid of a sensor device. The required adjustment of the motor is determined through comparison with the desired target combustion chamber volume. A reset function for position determination is not needed in this embodiment.
Another preferred embodiment of the method is characterized in that the metering valve device is normally closed, and is opened for a predefined length of time by the control device, such that a specified amount of gas flows into the combustion chamber. The gas is taken, for example, from a gas cartridge that is exchangeably arranged in the fastener driving tool. The amount of gas may be modulated by varying the length of the opening time of the metering valve device.
Another preferred embodiment of the method is characterized in that a desired amount of driving energy, a minimally possible amount of driving energy, and/or a maximally possible amount of driving energy is indicated on the fastener driving tool. The particular amount of driving energy is indicated preferably with the aid of the aforedescribed indicator device.
Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawing.